Transmissive optical encoder

ABSTRACT

In one embodiment, an optical encoder includes a light source, a detector array and a code member. The detector array is positioned in spaced-apart relation to the light source and includes at least one detector set. Each of the at least one detector sets includes a plurality of detector elements. The code member 1) is positioned between the light source and the detector array, 2) is moveable with respect to the detector array along a displacement direction, and 3) defines a plurality of circular or elliptical openings through which light emitted by the light source is filtered to produce light spots that travel across the detector array as the code member moves with respect to the detector array. Other embodiments are also disclosed.

BACKGROUND

The motion of a moveable component (e.g., the direction and rate ofmovement of the moveable component) can often be characterized by meansof an optical encoder. In the case of an absolute optical encoder, or anoptical encoder that has been initially calibrated to a known position,an optical encoder can also be used to characterize the position of amoveable component.

Although optical encoders may take various forms, most can becharacterized as linear or rotary. As their respective names imply,linear encoders are used to provide an indication of linear motion (andsometimes position), whereas rotary encoders are used to provide anindication of rotary motion (and sometimes position).

Most optical encoders can also be characterized as transmissive orreflective. In a transmissive optical encoder, a light source and aphotodetector are positioned on opposite sides of a code member (e.g., acode strip or a code wheel). As the code member is moved by a movablecomponent, a plurality of windows in the code member cause thephotodetector to be illuminated with a varying pattern of light, whichpattern can then be correlated with the motion of the moveablecomponent. In a reflective optical encoder, a light source and aphotodetector are positioned on the same side of a code member. Then, asthe code member is moved by a moveable component, a plurality ofreflectors on the code member causes the photodetector to be illuminatedwith a varying pattern of light.

SUMMARY OF THE INVENTION

In one embodiment, an optical encoder comprises a light source, adetector array and a code member. The detector array is positioned inspaced-apart relation to the light source and comprises at least onedetector set. Each of the at least one detector sets comprises aplurality of detector elements. The code member 1) is positioned betweenthe light source and the detector array, 2) is moveable with respect tothe detector array along a displacement direction, and 3) defines aplurality of circular or elliptical openings through which light emittedby the light source is filtered to produce light spots that travelacross the detector array as the code member moves with respect to thedetector array.

In another embodiment, an optical encoder comprises a light source, adetector array, a code member, and first and second adders. The detectorarray is positioned in spaced-apart relation to the light source andcomprises at least one detector set. A first of the detector setscomprises first, second, third and fourth detector elements positionedin adjacent relationship. The code member 1) is positioned between thelight source and the detector array, 2) is moveable with respect to thedetector array along a displacement direction, and 3) defines aplurality of circular or elliptical openings through which light emittedby the light source is filtered to produce light spots that travelacross the detector array as the code member moves with respect to thedetector array. The first adder is operatively associated with the firstdetector element and the third detector element to subtract an outputsignal produced by the third detector element from an output signalproduced by the first detector element, thereby generating a firstoutput. The second adder is operatively associated with the seconddetector element and the fourth detector element to subtract an outputsignal produced by the fourth detector element from an output signalproduced by the second detector element, thereby generating a secondoutput.

In yet another embodiment, a method comprises 1) positioning a detectorarray in spaced-apart relation to a light source, the detector arraycomprising at least one detector set, with each detector set comprisingat least four detector elements; 2) positioning a code member betweenthe light source and the detector set so that the code member and thedetector array are moveable with respect to one another along adisplacement direction, the code member defining a plurality of circularor elliptical openings through which light emitted by the light sourceis filtered to produce light spots that travel across the detector arrayas the code member moves with respect to the detector array; and 3)combining output signals from at least a first pair of non-adjacentdetector elements of the detector array to produce a firstquasi-sinusoidal signal.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative and exemplary embodiments of the invention are shown in thedrawings, in which:

FIG. 1 is a perspective view of a first exemplary optical encoder,wherein the encoder has a detector array comprising a single detectorset;

FIG. 2 is a side view of the optical encoder illustrated in FIG. 1;

FIG. 3 is a plan view of a code wheel that may be utilized with theoptical encoder of FIG. 1;

FIG. 4 is a schematic representation of the detector array shown in FIG.1, showing how the individual detector elements thereof are connected toa pair of adders;

FIG. 5 is a graphical representation of the output signals produced bythe detector elements of the detector array shown in FIG. 1, with theabscissa indicating movement of the spot along the detector array andthe ordinate indicating the output of the various detector elements andadders;

FIG. 6(a) is a schematic representation of the path of the FIG. 1 lightspot along a displacement direction that is substantially parallel tothe width dimension of the detector array;

FIG. 6(b) is a schematic representation of the path of the FIG. 1 lightspot along a displacement direction that is inclined with respect to thewidth dimension of the detector array;

FIG. 7 is a perspective view of another embodiment of an opticalencoder, wherein the encoder has a detector array comprising twodetector sets; and

FIG. 8 is a schematic representation of the detector array shown in FIG.7, showing how the individual detector elements thereof are connected toa pair of adders.

DETAILED DESCRIPTION

An exemplary optical encoder 10 is shown in FIGS. 1 and 2 and comprisesa light source 12, and a detector array 13 positioned in spaced-apartrelation from the light source 12. The light source 12 may comprise anyof a wide range of light sources suitable for producing light 56 that isdetectable by the detector elements 16 forming the detector array 13. Itis generally preferred, but not required, that the light source 12produce a collimated, or substantially collimated, beam 62 of light 56.Such a collimated beam 62 may be produced by the light source 12, or maybe formed with the aid of a separate collimating lens (not shown).

By way of example, in one embodiment, the light source 12 comprises alight emitting diode 64. The light emitting diode 64 may be providedwith an integral collimating lens 66 suitable for substantiallycollimating the light 56 produced by the light emitting diode 64 to formthe light beam 62. Alternately, a separate collimating lens (not shown)could be used.

The light source 12 may be mounted to a frame or housing (not shown)suitable for holding the light source 12 in spaced-apart relation to thedetector array 13. However, because various mounting arrangements of thelight source 12 could be easily provided by persons having ordinaryskill in the art after having become familiar with the teachingsprovided herein, the mounting arrangement of the light source 12 willnot be described in further detail herein.

The detector array 13 is positioned in spaced-apart relation to thelight source 12 and comprises at least one detector set 14. By way ofexample, FIGS. 1 and 2 show the detector array 13 to comprise a singledetector set 14. However, additional detector sets may be provided, aswill be described in greater detail later in this description.

Regardless of the number of detector sets 14 in the detector array 13,each detector set 14 comprises a plurality of individual detectorelements 16 that are positioned in a side-by-side adjacent relationshipalong the width direction 18 of the detector array 13. See FIG. 1. Byway of example, the detector set 14 comprises four (4) individualdetector elements 16: a first detector element 32, a second detectorelement 34, a third detector element 36, and a fourth detector element38. However, in alternate embodiments, the detector set 14 couldcomprise more than four (4) individual detector elements 16. Together,the detector elements 32, 34, 36, and 38 of the detector set 14 define awidth 28 of the detector set 14.

The individual detector elements 16 (e.g., first, second, third, andfourth detector elements 32, 34, 36, and 38) may comprise any of a widerange of devices suitable for detecting the light 56 produced by thelight source 12. However, by way of example, and in one embodiment, thevarious individual detector elements 16 forming the detector set 14comprise photodiodes.

The various individual detector elements 16 may be mounted to any of awide variety of structures, such as a printed circuit board 68, suitablefor holding the various detector elements 16 at the proper positionsalong the width direction 18 to form the detector set 14. Alternately,other mounting arrangements are possible, as would become apparent topersons having ordinary skill in the art after having become familiarwith the teachings provided herein.

It should be noted that in the embodiment illustrated in FIG. 1, whereinthe detector array 13 comprises a single detector set 14, the width 29of the detector array 13 will be the same as the width 28 of thedetector set 14. However, this will not be the case if the detectorarray 13 comprises more than one detector set 14. For example, and aswill be described with reference to an embodiment of an optical encoder110 illustrated in FIG. 7, if a detector array 113 comprises twodetector sets 114, then the width 129 of the detector array 113 will betwice the width 128 of the detector set 114. In some cases, and as willbe discussed later in this description, the width 29 of the detectorarray 13 may be used to determine the sizes and spacing of openings 22provided in the code member 20.

The code member 20 is positioned between the light source 12 and thedetector array 13 in the manner best seen in FIGS. 1 and 2 so that thecode member 20 and the detector array 13 are moveable with respect toone another along the displacement direction 24. In one arrangement, thecode member 20 may be mounted to a moveable component (not shown), andthe light source 12 and detector array 13 may be fixed in stationarypositions. In another arrangement, the code member 20 may be fixed, andthe light source 12 and detector array 13 may be mounted to a moveablecomponent. Regardless of the particular arrangement, the optical encoder10 detects the relative movement between the code member 20 and thedetector array 13.

The code member 20 may take on any of a wide range of forms orconfigurations, depending on its application. For example, if theoptical encoder 10 is to be used as a linear encoder, the code member 20may take the form or configuration of a generally elongate, strip-likemember 74, with the various openings 22 being arranged along a line, asbest seen in FIG. 1. Alternately, if the optical encoder 10 is to beused as a rotary encoder, the code member 20 may take the form orconfiguration of a disc-like member or “wheel” 70, with the variousopenings 22 being arranged in a generally circular manner around theperiphery of the wheel 70. See FIG. 3. Accordingly, the term “codemember”, as used herein, should not be regarded as limited to anyparticular shape or configuration of code member, but should instead bebroadly construed to include a linear code strip, a circular code“wheel,” or any other form or configuration of code member which may berequired or desired in a particular application.

The code member 20 is provided with a plurality of openings 22. Theopenings 22 may comprise any of a wide range of shapes. As will bedescribed in more detail later in this description, circular orelliptical shapes may enable the optical encoder 10 to produce one ormore quasi-sinusoidal waveforms (e.g., output signals 52 and 54 fromadders 40 and 42, respectively). Typically, circular openings will bestenable the adders 40 and 42 to provide outputs 52 and 54 most closelymatching true sinusoidal waveforms. However, openings that form ellipsesin a direction 78 that is perpendicular to the displacement direction 24can be useful in providing a greater quantity of light for the detectorarray 13 to sense (while still enabling the adders 40 and 42 to producequasi-sinusoidal waveforms). For the remainder of this description, itwill be assumed that the openings 22 are circular.

When each opening 22 is aligned with the light beam 62 produced by thelight source 12, the opening 22 functions to reduce or narrow the sizeof the light beam 62 to produce a narrowed beam 72, as best seen in FIG.2. The narrowed beam 72 results in the formation of a spot 58 on thedetector array 13. See FIGS. 4 and 5. The size and shape of the openings22 provided in the code member 20 define the size and shape of thenarrowed beam 72, and thus the size and shape of the spot 58. If thebeam 62 produced by the light source 12 is substantially collimated, thesize of the spot 58 will be approximately equal to the size of theopenings 22. However, if the beam produced by the light source 12 is notcollimated (e.g., if the beam comprises diverging light rays), then thesize of the openings 22 may differ from (e.g., be smaller than) the sizeof the spot 58.

In order to provide the proper amount of spatial filtering, thedimension 26 of the spot 58 in the displacement direction 24 ispreferably less than the width 28 of the detector set 14, but greaterthan the width 76 of a single detector element 16. Even more preferably,the dimension of the spot 58 in the displacement direction 24 is about40% to about 80% of the width 28 of the detector set 14.

In addition to the size of the spot 58, the spacing between successivespots is preferably adjusted so that only a single spot 58 illuminatesthe detector array 13 at any given time. However, at least one spot 58should always illuminate the detector array 13. To eliminate motiondetection “gaps”, when the code member 20 is moving but no spot 58 ismoving across the detector array, it may sometimes be desirable to allowmore than one spot 58 to illuminate the detector array 13 at the sametime. However, in these cases, it is preferable to keep the multiplelight spots to “about one” light spot 58. As defined herein, “about one”light spot is defined to be less than or equal to one-and-a-half (1½)light spots 58.

To adjust the size and spacing of light spots 58 illuminating thedetector array 13, and for a given light source 12 and detector array13, the positions (i.e., spacings) of the light source 12, the detectorarray 13 and the code member 20 may be adjusted. In addition, the size26 and spacing 30 of the openings 22 in the code member 20 may beadjusted. If the light source 12 is a collimated light source, then thepositions (i.e., spacings) of the light source 12, the detector array 13and the code member 20 may be somewhat less critical, with the size andspacing of the light spots 58 being about equal to the size 26 andspacing 30 of the openings 22 in the code member 20.

Referring now primarily to FIGS. 4 and 5, the optical encoder 10 mayfurther comprise first and second adders 40 and 42 that are connected tothe various individual detector elements 16 forming the detector array13, so that the individual detector elements 16 are “interdigitated”.That is, alternating ones of the detector elements 16 may be connectedto different ones of the adders 40 and 42. In this manner, the codemember 20 and the detector array 13 form a “spatial filter”. Also, ifthe openings 22 in the code member 20 are circular or elliptical, theoutputs 52, 54 of the adders 40, 42 will comprise quasi-sinusoidalwaveforms, as best seen in FIG. 5.

More specifically, the first adder 40 is operatively connected to thefirst detector element 32 and the third detector element 36, whereas thesecond adder 42 is operatively connected to the second detector element34 and the fourth detector element 38. The first adder 40 combines theoutput signals of the first and third detector elements 32 and 36 bysubtracting the output signal 48 of the third detector element 36 fromthe output signal 44 of the first detector element 32. The resultingoutput signal 52 of the first adder 40 comprises a quasi-sinusoidalwaveform. See FIG. 5.

The second adder 42 combines the output signals of the second and fourthdetector elements 34 and 38 by subtracting the output signal 50 of thefourth detector element 38 from the output signal 46 of the seconddetector element 34. The resulting output signal 54 of the second adder42 comprises a quasi-sinusoidal waveform, as also best seen in FIG. 5.

A processing system 60 may be connected to the first and second adders40 and 42 so that the processing system 60 is responsive to the outputsignals 52 and 54 produced by the first and second adders 40 and 42. Theprocessing system 60 may then be operated to analyze the output signals52 and 54 from the first and second adders 40 and 42 in order to deriveinformation about the relative movement between the code member 20 andthe detector array 13. For example, the processing system 60 maydetermine the velocity (i.e., speed) of the motion between the codemember 20 and the detector array 13 by measuring the frequency of thequasi-sinusoidal waveform of either the output signal 52 from the firstadder 40 or the output signal 54 from the second adder 42. Theprocessing system 60 may also be used to determine the direction ofmotion between the code member 20 and the detector array 13, for exampleby measuring the phase difference or phase shift between thequasi-sinusoidal waveforms of the output signals 52 and 54. Of course,the processing system 60 may be used to determine other aspects of therelative motion between the code member 20 and the detector array 13 by,for example, integrating or differentiating the output signals 52 and54.

By way of example, in one embodiment, the processing system 60 maycomprise a general purpose programmable computer (e.g., a PC) that isprogrammed to sense the frequencies of the quasi-sinusoidal waveforms aswell as their phase difference, to make desired calculations, and toproduce desired output data. Alternately, the processing system 60 couldcomprise an application-specific integrated circuit (ASIC).

The optical encoder 10 may be operated as follows to detect relativemovement between the code member 20 and the detector array 13. Assumingthat the light source 12 and detector array 13 have been positioned inspaced-apart relation, and the code member 20 is positionedtherebetween, the optical encoder 10 may be used to measure the relativemovement between the code member 20 and the detector array 13. Forexample, in an arrangement wherein the code member 20 is mounted to amoveable component (not shown) and the detector array 13 remainsstationary, light 56 from the light source 12 will pass through anopening 22 provided in the code member 20 before illuminating thedetector array 13 at a spot 58. In one embodiment, the size of the spot58 is substantially the same as the size of the opening 22 provided inthe code member 20. The relative movement between the code member 20 andthe detector array 13 causes the spot 58 to be moved or scanned acrossthe individual detector elements 32, 34, 36, 38 of the detector array13. See FIG. 5.

As the spot 58 illuminates each detector element 32, 34, 36, 38, theilluminated detector element (or elements) produces an output signalthat is related to the amount of light incident thereon. For example,and with reference to FIG. 5, the movement of the spot 58 across eachsuccessive detector element 32, 34, 36, 38 comprising the detector array13 results in each detector element 32, 34, 36, 38 producing an outputsignal having a quasi-sinusoidal pulse. More specifically, the first,second, third, and fourth detector elements 32, 34, 36, 38 producecorresponding output signals 44, 46, 48, 50 comprising quasi-sinusoidalpulses, with each pulse being shifted (i.e., delayed in time) in amanner that corresponds to the movement of the spot 58 across thedetector array 13.

The quasi-sinusoidal pulses output by the various detector elements 32,34, 36, and 38 are combined by the first and second adders 40 and 42 toproduce quasi-sinusoidal waveforms corresponding to output signals 52and 54. More specifically, the first adder 40 subtracts the third outputsignal 48 from the first output signal 44 to produce thequasi-sinusoidal output signal 52 (i.e., the “I” channel), whereas thesecond adder 42 subtracts the fourth output signal 50 from the secondoutput signal 46 to produce the quasi-sinusoidal output signal 54 (i.e.,the “Q” channel).

The processing system 60 may then be used to analyze the output signals52 and 54 from the first and second adders 40 and 42 to deriveinformation relating to the relative movement of the code member 20 andthe detector array 13. For example, the relative velocity or speedbetween the code member 20 and the detector array 13 may be determinedby the processing system 60 based on a frequency of the output signal(e.g., 52 or 54) from one of the first and second adders 40 and 42. Thatis, the frequency of the quasi-sinusoidal waveform corresponding to theoutput signal 52 of the first adder 40 is related to the relativevelocity between the code member 20 and the detector array 13. Likewise,the frequency of the quasi-sinusoidal waveform corresponding to theoutput signal 54 of the second adder 42 is also related to the relativevelocity between the code member 20 and the detector array 13. Thus, avelocity or speed determination may be made by measuring the frequencyof the output signal 52 of the first adder 40, the output signal 54 ofthe second adder 42, or various combinations thereof.

The direction of movement of the code member 20 with respect to thedetector array 13 may be determined from the phase relationship or phasedifference between the quasi-sinusoidal waveforms 52 and 54 of the firstand second adders 40 and 42. More specifically, in the embodiment shownand described herein, the “I” and “Q” channels will be 90° out-of-phase.Therefore, if the “I” channel leads the “Q” channel by 90°, the relativemotion between the detector array 13 and code member 20 will be in afirst direction. If the “I” channel lags the “Q” channel by 90°, therelative motion between the detector array 13 and the code member 20will be in a direction opposite the first direction. In addition, otherinformation about the relative movement between the code member 20 andthe detector array 13 may be determined by integrating ordifferentiating the output signals 52 and 54 produced by the adders 40and 42.

As mentioned above, the detector array 13 may comprise more than oneindividual detector set 14. Providing additional detector sets 14 canprovide for increased spacing between the adjacent openings 22 providedin the code member 20, which can be advantageous in some circumstances.Referring now to FIGS. 7 and 8, a second embodiment 110 of an opticalencoder comprises a light source 112 and a detector array 113 positionedin spaced-apart relation. The detector array 113 in this embodimentcomprises two detector sets 114, each of which comprises four (4)individual detector elements 116. A code member 120 positioned betweenthe light source 112 and the detector array 113 is provided with aplurality of openings 122.

As with the optical encoder 10, when the light source 112 illuminatesthe code member 112, a light spot or spots 158 illuminate the detectorarray 113. In order to provide the proper amount of spatial filtering,the dimension of the spot 158 in the displacement direction 124 ispreferably less than the width 128 of one detector set 114, but greaterthan the width of a single detector element 116. Even more preferably,the dimension of the spot 158 in the displacement direction 124 is about40% to about 80% of the width 128 of one detector set 114.

In addition to the size of the spot 158, the spacing between successivespots is preferably adjusted so that only a single spot 158 illuminatesthe detector array 113 at any given time. However, at least one spot 58should always illuminate the detector array 13. To eliminate motiondetection “gaps” when the code member 120 is moving but no spot 158 ismoving across the detector array, it may sometimes be desirable to allowmore than one spot 158 to illuminate the detector array 113 at the sametime. However, in these cases, it is preferable to keep the multiplelight spots to “about one” light spot 158. As defined herein, “aboutone” light spot is defined to be less than or equal to one-and-a-half(1½) light spots 158.

To adjust the size and spacing of light spots 158 illuminating thedetector array 113, and for a given light source 112 and detector array113, the positions (i.e., spacings) of the light source 112, thedetector array 113 and the code member 120 may be adjusted. In addition,the size 126 and spacing 130 of the openings 122 in the code member 120may be adjusted. If the light source 112 is a collimated light source,then the positions (i.e., spacings) of the light source 112, thedetector array 113 and the code member 120 may be somewhat lesscritical, with the size and spacing of the light spots 158 being aboutequal to the size 126 and spacing 130 of the openings 122 in the codemember 120.

Referring now primarily to FIG. 8, the detector array 113 comprises atotal of eight individual detector elements 116: first, second, third,and fourth detector elements 132,134, 136, and 138, respectively, whichtogether form a first detector set 114, and fifth, sixth, seventh, andeighth detector elements 132′, 134′, 136′, and 138′, respectively, whichtogether form a second detector set 114. The various detector elements116 are also “interdigitated.” More specifically, the first and fifthdetector elements 132 and 132′ are connected together and to a firstadder 140. The third and seventh detector elements 136 and 136′ areconnected together and to the first adder 140. The first adder 140combines the signals from the detectors in the manner already describedfor the adder 40 of the first embodiment 10. That is, the first adder140 subtracts the combined signals from the third and seventh detectors136 and 136′ from the combined signals from the first and fifth detectorelements 132 and 132′ to produce a quasi-sinusoidal output signal 152.

The second and sixth detector elements 134 and 134′ are connectedtogether and to a second adder 142. The fourth and eighth detectorelements 138 and 138′ are connected together and to the second adder 142in the manner illustrated in FIG. 8. The second adder 142 combines thesignals from the various detectors in the manner already described forthe adder 42 of the first embodiment 10. That is, the second adder 142subtracts the combined signals from the fourth and eighth detectorelements 138 and 138′ from the combined signals from the second andsixth detector elements 134 and 134′ to produce a quasi-sinusoidaloutput signal 154.

A processing system 160, operatively connected to the first and secondadders 140 and 142, processes the first and second quasi-sinusoidalsignals 152 and 154 in the manner already described to produceinformation relating to the relative movement of the code member 120 anddetector array 113.

In most applications, the optical encoders 10 and 110 may be used toproduce quasi-sinusoidal output signals without the need to utilize aseparate reticle. Besides adding to an encoder's component count, aseparate reticle is difficult to properly align. In addition, thespatial filters formed by the combinations of the detector arrays andopenings in the code members 20 and 120 provide for increased resolutionover conventional encoder designs. The code members 20 and 120 andspatial filters of the optical encoders 10 and 110 also enable theoptical encoders 10 and 110 to better tolerate misalignments of the codemembers 20 and 120 and detector arrays 13 and 113. For example, andreferring to FIGS. 6(a) and 6(b), it is generally desirable for thedisplacement direction 24 to be generally parallel to the widthdirection 18 of the detector array 13, as best seen in FIG. 6(a).However, the optical encoder 10 of the present invention will providesatisfactory operation even in the case of a non-parallel displacementdirection 26′ (i.e., even though the displacement direction 26′ may betilted or inclined with respect to the width direction 18 of thedetector array 13 by an angle θ). Such non-parallel alignment may be theresult of accumulated tolerance errors or other misalignments that mayoccur during production or operation.

1. An optical encoder, comprising: a light source; a detector arraypositioned in spaced-apart relation to the light source, the detectorarray comprising at least one detector set, and each of the at least onedetector set comprising a plurality of detector elements; and a codemember positioned between the light source and the detector array, thecode member and the detector array being moveable with respect to oneanother along a displacement direction, and the code member defining aplurality of circular or elliptical openings through which light emittedby the light source is filtered to produce light spots that travelacross the detector array as the code member moves with respect to thedetector array.
 2. The optical encoder of claim 1, wherein the lightsource, the detector array and the code member are positioned, and theopenings in the code member are sized, to cause the light spots to havedimensions along the displacement direction that are less than a widthof one of the detector sets, but greater than a width of one of thedetector elements.
 3. The optical encoder of claim 2, wherein the lightsource, the detector array and the code member are positioned, and theopenings in the code member are spaced, to cause about one light spot toilluminate the detector array at a time.
 4. The optical encoder of claim2, wherein the light source, the detector array and the code member arepositioned, and the openings in the code member are spaced, to causeonly one light spot to illuminate the detector array at a time.
 5. Theoptical encoder of claim 1, wherein the light source, the detector arrayand the code member are positioned, and the openings in the code memberare sized, to cause the light spots to have dimensions along thedisplacement direction in a range of about 40% to about 80% of a widthof one of the detector sets.
 6. The optical encoder of claim 1, wherein:the light source is a collimated light source; and each of the openingsdefined by the code member has a dimension along the displacementdirection that is less than a width of one of the detector sets, butgreater than a width of one of the detector elements.
 7. The opticalencoder of claim 6, wherein each of the openings defined by the codemember is separated from an adjacent opening by a distance that is aboutequal to a width of the detector array.
 8. The optical encoder of claim1, wherein: the light source is a collimated light source; and each ofthe openings defined by the code member has a diameter along thedisplacement direction in a range of about 40% to about 80% of a widthof one of the detector sets.
 9. The optical encoder of claim 1, whereinthe light source comprises a light emitting diode.
 10. The opticalencoder of claim 1, wherein each of the detector elements comprises aphotodiode.
 11. The optical encoder of claim 1, wherein the at least onedetector set comprises a first detector set, the first detector setcomprising first, second, third and fourth detector elements positionedin adjacent relationship; the optical encoder further comprising: afirst adder, operatively associated with the first detector element andthe third detector element to subtract an output signal produced by thethird detector element from an output signal produced by the firstdetector element, thereby generating a first output; and a second adder,operatively associated with the second detector element and the fourthdetector element to subtract an output signal produced by the fourthdetector element from an output signal produced by the second detectorelement, thereby generating a second output.
 12. The optical encoder ofclaim 11, wherein: the at least one detector set further comprises asecond detector set, the second detector set comprising fifth, sixth,seventh and eighth detector elements positioned adjacent the detectorelements of the first detector set; the first adder adds to its outputan output signal produced by the fifth detector element less an outputsignal produced by the seventh detector element; and the second adderadds to its output an output signal produced by the sixth detectorelement less an output signal produced by the eighth detector element.13. The optical encoder of claim 11, further comprising a processingsystem that is operatively associated with the first and second adders,the processing system determining a speed of relative movement betweenthe code member and the detector array based on a frequency of an outputsignal from one of the first and second adders.
 14. The optical encoderof claim 11, further comprising a processing system that is operativelyassociated with the first and second adders, the processing systemdetermining a direction of relative movement between the code member andthe detector array based on a phase difference between the respectivefirst and second outputs of the first and second adders.
 15. The opticalencoder of claim 1, wherein the code member comprises an elongatemember, and wherein the plurality of openings defined by the code memberare positioned along a line.
 16. The optical encoder of claim 1, whereinthe code member comprises a disc-like member, and wherein the pluralityof openings defined by the code member are positioned around a peripheryof the disc-like member.
 17. An optical encoder, comprising: a lightsource; a detector array positioned in spaced-apart relation to thelight source, the detector array comprising at least one detector set,and a first of the detector sets comprising first, second, third andfourth detector elements positioned in adjacent relationship; a codemember positioned between the light source and the detector array, thecode member and the detector array being moveable with respect to oneanother along a displacement direction, and the code member defining aplurality of circular or elliptical openings through which light emittedby the light source is filtered to produce light spots that travelacross the detector array as the code member moves with respect to thedetector array; a first adder, operatively associated with the firstdetector element and the third detector element to subtract an outputsignal produced by the third detector element from an output signalproduced by the first detector element, thereby generating a firstoutput; and a second adder, operatively associated with the seconddetector element and the fourth detector element to subtract an outputsignal produced by the fourth detector element from an output signalproduced by the second detector element, thereby generating a secondoutput.
 18. A method, comprising: positioning a detector array inspaced-apart relation to a light source, the detector array comprisingat least one detector set, with each detector set comprising at leastfour detector elements; positioning a code member between the lightsource and the detector set so that the code member and the detectorarray are moveable with respect to one another along a displacementdirection, the code member defining a plurality of circular orelliptical openings through which light emitted by the light source isfiltered to produce light spots that travel across the detector array asthe code member moves with respect to the detector array; and combiningoutput signals from at least a first pair of non-adjacent detectorelements of the detector array to produce a first quasi-sinusoidalsignal.
 19. The method of claim 18, wherein the light source, the codemember and the detector array are positioned, and the openings in thecode member are sized and spaced, to cause the openings in the codemember to produce light spots on the detector array that i) havedimensions along the displacement direction that are less than a widthof one of the detector sets, but greater than a width of one of thedetector elements, and ii) are separated from adjacent light spots bydistances that are about equal to a width of the detector array.
 20. Themethod of claim 18, further comprising, determining a speed of relativemovement between the code member and the detector array based on afrequency of the first quasi-sinusoidal signal.
 21. The method of claim18, wherein combining the output signals from at least the first pair ofnon-adjacent detector elements comprises subtracting the output signalsfrom each other.
 22. The method of claim 18, further comprising,combining output signals from at least a second pair of non-adjacentdetector elements to produce a second quasi-sinusoidal signal, thesecond pair of non-adjacent detector elements being interdigitated withthe first pair of non-adjacent detector elements.
 23. The method ofclaim 22, further comprising, determining a direction of relativemovement between the code member and the detector array based on a phasedifference between the first and second quasi-sinusoidal signals. 24.The method of claim 22, wherein combining the output signals from atleast the second pair of non-adjacent detector elements comprisessubtracting the output signals from each other.